1. Field of the Invention
The present invention relates to a mobile communication system, a base station, a radio network controller, and a resource allocation control method used therefor. In particular, the present invention relates to allocation of resources such as codes from a radio network controller to a base station in HSDPA (High Speed Downlink Packet Access).
2. Description of the Prior Art
A mobile communication system such as the W-CDMA (Wideband-Code Division Multiple Access) system uses HSDPA which is a high speed downlink transmission system. In the case in which the HSDPA is provided, it is necessary to set an HS-PDSCH (High Speed-Physical Downlink Shared Channel) and a DPCH (Dedicated Physical Channel) in a downstream.
Here, the DPCH is an individual channel for sending control data. In particular, the DPCH, which is set in controlling the HS-PDSCH, is called an Associated DPCH. It is possible to set the DPCH independently, and user data can be sent on the DPCH. The HS-PDSCH is a channel for sending user data as a packet and is shared by a plurality of users in a time multiplex manner.
An RNC (Radio Network Controller) allocates codes to an HS-PDSCH and DPCHs of a base station (e.g., see 3GPP TS25.433 V5.1.0 (2002-06), Chapter 8.2.18″). A code indicates a channelization code which is used for identification of each physical channel in a downlink.
The base station controls transmission power of the HS-PDSCH and the DPCHs on the basis of transmission power value of the HS-PDSCH notified from the RNC and sets the HS-PDSCH between the base station and mobile stations using codes allocated by the RNC (hereinafter referred to as allocated codes) and the above-described transmission power (hereinafter referred to as allocated power). The DPCHs are used for the setting of the HS-PDSCH.
However, although the base station cannot use the codes allocated to the HS-PDSCH for the DPCHs, the power allocated to the HS-PDSCH can also be used for the DPCHs in the above-described transmission power control. In the case in which the DPCHs use the power allocated to the HS-PDSCH, transmission power of the HS-PDSCH is decreased such that a sum of transmission power of the HS-PDSCH and transmission power of the DPCHs does not exceed a maximum transmission power of the base station.
Closed loop transmission power control is applied to transmission power of respective DPCHs such that reception qualities of the DPCHs in the mobile stations are uniform. The mobile stations measure a channel quality using a down channel [CPICH (Common Pilot Channel), etc.] and inform the base station of channel quality information (CQI: Channel Quality Indication).
The base station performs control of an AMCS (Adaptive Modulation and Coding Scheme), the number of codes, and the like on the basis of the channel quality information from the mobile stations. In addition, the base station performs scheduling in sending data on the HS-PDSCH.
The number of allocated codes in the above-described HS-PDSCH indicates the maximum number of codes which the base station can use for the HS-PDSCH. The allocated power of the HS-PDSCH indicates a maximum power which the base station can use for the HS-PDSCH in the transmission power control.
By limiting the number of codes and power allocated to the HS-PDSCH, a TBS (Transport Block Size), that is, OTA (Over the Air) throughput is limited. The TBS indicates an available transfer data amount which is found from the above-described number of codes, the transmission power, and the channel quality information. The OTA throughput indicates the number of bits which can be sent in a unit time (transmission speed).
If the channel quality information, the number of codes, a modulation system, and a coding rate are determined, the base station can estimate transmission power which is required for satisfying a predetermined PER (Packet Error Rate). For example, in the case in which a channel quality is defined as a reception CINR (Carrier to Interference and Noise Ratio) of the CPICH, transmission power PHS-PDSCH required by the HS-PDSCH is represented by an expression described below.PHS-PDSCH=PCPICH×[requiredSINR/SF]HS-PDSCH/[CINR]CPICH 
Here, [requiredSINR] is an SINR (Signal to Interference and Noise Ratio) required for satisfying the predetermined PER and varies depending upon a combination of the number of codes, the modulation system, and the coding rate.
In the conventional transmission power control, the base station allocates the power to the DPCHs on the basis of the power of the HS-PDSCH which is notified from the RNC. Since the power of the HS-PDSCH can also be used for the DPCHs, it is unclear for the RNC to which degree the base station actually uses the power of the HS-PDSCH, which has been notified from the RNC.
Similarly, it is unclear for the RNC which degree of power the base station actually uses for the DPCHs. In other words, the RNC cannot learn to which degree the base station actually uses the power of the HS-PDSCH unless the RNC is informed from the base station.
In the transmission power control of the base station, if the power of the HS-PDSCH is increased, the power is not used efficiently, and power to be allocated to the DPCHs becomes insufficient. In the case in which the power to be allocated to the DPCHs is insufficient, since the number of mobile stations in which the Associated DPCH can be set decreases, the HS-PDSCH cannot be used effectively, and a system capacity of the base station decreases.
Conversely, in the case in which the power of the HS-PDSCH is too small, regardless of the fact that the capacity of the HS-PDSCH is small, since power to be allocated to the Associated DPCH increases, the number of mobile stations, which can receive an HSPDA service, increases, and convergence occurs in the HSPDA service.
In the case in which power is distributed to the HS-PDSCH and the DPCHs appropriately, the RNC is required to grasp a state of use of the power in the base station. As a method therefor, there is a method with which the base station calculate the average amount of use of power and inform the RNC of the calculated value. For example, in 3GPP (3rd Generation Partnership Project), Transmitted Carrier Power for measuring a total value of transmission power of all channels in average is defined as Common Measurement (e.g., see 3GPP TS25.133 V5.2.0 (2002-03), Chapter 9.2.4).
The above-described code allocation method also has the same problem as the distribution of power. The RNC allocates codes to the HS-PDSCH of the base station and also allocates codes to the DPCHs. However, the RNC cannot learn to which degree the base station actually uses the codes allocated to the HS-PDSCH unless the RNC is informed from the base station.
In this code allocation, in the case in which codes to be allocated to the HS-PDSCH are too many, the codes are not used effectively, and codes to be allocated to the DPCHs become insufficient. Thus, the Associated DPCH for controlling the HS-PDSCH cannot be set. Since the number of mobile stations which can receive an HSPDA service decreases, the HS-PDSCH cannot be used effectively, and the system capacity of the base station decreases.
In addition, in the case in which codes to be allocated to the HS-PDSCH is too few, regardless of the fact that a transmission speed of the HS-PDSCH is low, since the number of users, for which the Associated DPCH can be set, increases, the number of mobile stations which can received an HSPDA service increases, and convergence occurs in the HSPDA service.
Therefore, in the case in which codes are allocated to the HS-PDSCH and the DPCHs appropriately, the RNC is required to grasp a state of use of codes in the base station. A method with which the base station calculates the average number of use of codes and which informs the RNC of the calculated value is possible.
In the above-described conventional resource allocation control method, in the case in which codes are distributed to the HS-PDSCH and the DPCHs appropriately, it is conceivable to calculate the average number of use of codes and inform the calculated value from the base station to the RNC. However, if an average value is informed including the number of use of codes at the time when a packet is not sent or a time when data to be sent is little, the informed value varies significantly depending upon a ratio of the time when a packet is not sent.
In addition, in the case in which data is little, since the number of codes to be allocated in the RNC decreases, the base station cannot grasp the number of available codes, which is limited by the maximum transmission power of the HS-PDSCH.
Moreover, a scheduling method varies depending upon a base station, and it is possible that a base station, which allocates all codes to a transmission packet, and a base station, which uses fewer codes in order to control a variation range of transmission power when convergence does not occur, are mixed. In the case in which these base stations are mixed, even if the average value is the same, the RNC cannot grasp whether a packet is sent using all the allocated number of codes or intentionally using the fewer number of codes if the RNC does not know the scheduling method of the base station.
Furthermore, in the case in which a system capacity of the base station is small compared with the number of HSDPA users, it is unclear for the RNC how many allocated codes should be increased. Therefore, in order to distribute codes appropriately to the HS-PDSCH and the DPCHs, the RNC is required to grasp information on a state of use of allocated codes.
Similarly, in order to notify an appropriate value in notifying power, which should be used for the HS-PDSCH, to the base station, the RNC is required to grasp information on a state of use of allocated power in the base station.
On the other hand, in the case in which codes and power to be allocated to the HS-PDSCH are too little, since convergence occurs in the HSPDA service, in order to distribute codes appropriately to the HS-PDSCH and the DPCHs, the RNC is required to grasp information on a state of use of an HS-PDSCH channel.